1. Field of the Invention
The present invention relates generally to extrusion cooking systems, and in particular to an enhanced hydration subsystem for providing a high-starch slurry to the extrusion cooking system for improving extrusion cooking performance and the characteristics of the finished products.
2. Description of the Related Art
Extrusion cooking systems are commonly used for a wide variety of products and include extruders of various configurations wherein feed materials are cooked and formed to produce various finished products, such as animal feed and food products for human consumption. Such extrusion systems can be adjusted for a wide variety of operating conditions according to the requirements of particular applications. For example, factors such as product density (for floating or sinking aquaculture feed products), starch content, protein levels, oil content and fat content can be adjusted as necessary to produce desired finished products.
By way of example, aquaculture feed products comprise a class of feed materials which are particularly well suited for extrusion manufacture. There is considerable demand for such products in the aquaculture industry, which requires feed materials having certain nutrient and other characteristics for optimizing aquaculture growth. For example, aquaculture growth can be enhanced by providing relatively high oil content in the feed products.
It is often desired that such feed products have specific gravities greater than 1.00 so that they will sink upon dispersal in a body of water containing aquacultures such as fish or shrimp. Such sinking feed products are often preferred for types of aquaculture which tend to bottom feed because such feed materials tend to be consumed more rapidly and are thus less susceptible to waste and spoilage. The water inhabited by such aquaculture thus tends to remain cleaner and healthier.
A common problem with extruding sinking fish feed relates to the effects of extrusion cooking on materials with relatively high starch contents, which are commonly required to provide the resulting feed materials with necessary nutritional values. The problem is that in the extruder the starches tend to expand upon cooking, thus reducing the product density. Moreover, extrusion cooking can be somewhat inefficient if all of the starches in the materials must be gelatinized in the extrusion cooking stage.